Shell mold and method of making same



Oct. 1, 1957 J. c. sAwYER 2,807,845

SHELL MoLD AND METHOD oF MAKING SAME Filed April 7, 1953 2 Sheets-Sheet 1 v :gli:

j [4 )5. /6 /65 I4 HD 2 5-272172271 daf/N C 64M/f( Oct. l, 1957 l J. c. sAwYER SHELL MOLD AND METHOD OF MAKING SAME 2 Sheets-Sheet 2 Filed April 7. 1953 United States Patent l" SHELL MOLD AND METHOD or MAKING SAME .lohn C. Sawyer, Cleveland Heights, Ohio, assignor to Thompson Products, Inc., Cleveland, Ohio, a corporation of Ohio Application April 7, 1953, Serial No. 347,378

6 Claims. (Cl. 22-130) This invention relates to the production of molds. Specifically, this invention deals with molds composed of bonded sand such as are used in the so-called shell mold casting art.

Heretofore, shell molds have been prepared by depositing a mixture of thermosetting binder and sand on a heated pattern to soften the binder and bond the sand particles together thereby forming a continuous shell or coating over the pattern. The excess unbonded sand mixture on the pattern is then removed by inverting the assembly so as to allow the free sand particles to drop off of the coating. A relatively thin coating is thus formed having a rough outside face generally following the contour of the pattern. In this procedure, the thickness of the coating or shell is controlled by the degree of heat penetration from the pattern into the binder and sand mixture and is usually less than one quarter of an inch. If substantially thicker molds were attempted, they would not cure evenly in the subsequent heat treatment which is used to completely set the thermosetting binder. The relatively thin molds, after being completely cured, are conventionally held in face-to-face engagement and are backed up by steel shot or other suitable lling material which will follow the irregular outside face of the mold to give support thereto. The liquid metal to be cast is then poured into the mold cavity in the conventional manner.

Due to the necessity for freeing the outer face of the mold from the unset sand particles, the forming machines to produce these shell molds must be equipped with turning mechanisms so that the free excess sand on the pattern could drop off by gravity action.

The present invention now provides a shell mold with a smooth outside face which is useful in providing a mold cavity-closingface thereby accommodating the stacking together of a plurality of the molds to provide a succession of mold cavities each partially defined by an outside face of an adjacent mold.

Another feature of this present invention resides in the formation of a shell mold having a smooth, flat back face and a mold cavity of any desired depth without increasing the Wall thickness of the shell beyond a desired thickness.

Another feature of the invention is to provide a mold pattern which has an insert plate surrounding its mold cavity-defining portion to decrease the thickness of the resulting mold in the areas of the mold surrounding the mold cavity.

Another important feature of this invention is to provide molds of flatter contour 'than heretofore possible, by curing the molds simultaneously from opposite faces.

A further feature of the invention resides in the provision of a shell mold which has the mold cavity-defining walls thereof surrounded by hollowed-out portions which portions in turn, are surrounded by a rigidifying maginal flange so that the molds can be easily stacked to provide safety reservoirs for molteny metal in the event that a mold cavity-defining wall should break away.

Another important feature of the invention relates to ICC the provision of plate-like shell molds each having its own sprue and adapted to be stacked to coact with the next adjacent plate to produce the full sprue.

Another feature of the invention resides in the provision of a method of making shell molds which does not require inversion of the mold to remove excess sand from the back face of the mold.

lt is then a very important object of this invention to provide plate-like shell molds adapted to be stacked for forming a series of mold cavities and not requiring the heretofore necessary backing material to support the shells.

Another object of this invention is to provide a shell mold having a marginal flange, ribs within the marginal flange dening the mold cavity, and hollow spaces between the flange and ribs forming reservoirs for molten metal in the event of breakthrough or leakage beyond the ribs.

Another important object of this invention is to provide a method of making molds from resin-impregnated particulate earth-like material such as silica or zircon sand, which involves the'use of a pattern having a filter plate to create a hollow cavity beyond the mold cavity-defining wall.

A further object of this invention is to provide a resinbonded sand plate mold with a central sprue adapted to register with the sprues in similar plate molds to produce a stack of molds fed from a single sprue.

Other and further objects and features of this invention will be apparent to those skilled in the art from the following detailed description of the annexed sheets of drawings which, by way of a preferred example, illustrate one embodiment of the invention.

On the drawings:

Figure l is a plan view of a pattern for forming a plate mold according to this invention.

Figure 2 is a vertical cross-sectional view with a part in elevation, taken along the line II-II of Figure 1 and showing the pattern filled with a thermosetting resin and sand mixture in particulate form.

Figure 3 is a vertical cross-sectional view taken along the line III-III of Figure 1 but illustrating the pattern filled with resin-impregnated sand and having a cover plate thereon to form a smooth top face for the mold.

Figure 4'is a plan View of the sand mold formed as illustrated in Figure 3.

Figure 5 is a vertical cross-sectional View taken along the line V-V of Figure 4.

Figure 6 is a vertical cross-sectional view, with parts in elevation, illustrating the manner in which the molds of Figures 4 and 5 are stacked and clamped together to provide a series of mold cavities filled from a common sprue.

'As shown on the drawings:

The pattern 10 as illustrated in Figures l to 3 is for the purpose of forming resin-bonded sand molds in plate form and having four mold cavities of valve seat insert ring configurations fed from a central sprue. Valve seat insert rings for internal combustion engines are cast from expensive high-temperature and corrosion-resisting alloys that are dificult to grind and machine and the present invention forms castings in an almost finished state thereby minimizing the expensive heretofore necessary machining and` grinding. Itwill be understood, of course, that the invention is not limited to the casting of any specific shape.

The illustrated pattern plate 1f! includes a square box ory the inner face of the side wall 11a as shown in Figure l.

Patented Oct. 1, 195,7l

This gap G should be of sucient width to form therebetween a self-sustaining peripheral flange on the mold to be formed.

The filler plate 12 has al cloverleaf-shaped centrall cavity 12a with four lobes of fragmental circular contour. Pushout pin holes 12b with counterbores to provide for pushout pin heads are provided between the lobes of the cavity 12a. As shown in Figure 2, the plate 12 hasa attop 12C terminating at a level beneath the top edge of the side wall 11a. Y

Within the cloverleaf cavity 12a of the plate 12, there are provided upstanding mold cavity-defining patterns integral with or attached to the bottom wall 11b of the pattern plate 11. These patterns are spaced inwardly from the edges of the cavity 12a and comprise a circular ring 13 in each lobe of the cut-out portion terminating in a Hat. top at a level beneath the top edge of the side wall 11a, and a tapered plug 14 in spaced concentric relation within the ring 13 and projecting above the level of the ring 13 to terminate at a dat top beneath the top edge of the side wall 11a. A central tapered plug 15 is provided in the center of the space surrounded by the rings 13 and this central plug projects to a level thatfmay be flush with thetop edge of the side wall 11a. A separateV runner and gate-forming pattern 16 extends from the plug 15 to each ring pattern 13 as shown in Figures l, 2 and 3 and has an outer end portion converging both in width and in height to form a narrow and relatively thin connecting gate 16a against the outer face of the ring 13 at the bottom thereof.

Four ring-shaped mold cavities are formed by this arrangement, each dened by a ring 13, and surrounded by concentric cavities created between the outer face of the ring pattern 13 and the adjoining edge wall of the cavity 12a of the plate 12 and by the space between the plug 14 and the inner face of the ring 13. The plug 14, of course, forms a blind cavity in the resulting mold.

As shown. in Figures 2 and 3, the rings 13 have the same height as the plate 12 while the plugs 14 may extend to levels above the rings 13 and the central plug 15is at a higher level than the plugs 14 or rings 13. In addition, the runner-forming patterns 16 at the ends thereof adjacent the plug 15 may be at levels higher than the rings 13 but at levels lower than the edge of the side wallsr 11a.

The bottom wall 11b of the pattern box 11 has holes such as 11C therethrough in alignment with the holes 12b of the filler plate 12 to receive ejector pins such as 17 in slidable relation therethrough. The pins 17 have heads 17a tting in the counterbores of the holes 12b of the plate 12.

As shown in Figure 2, the pattern box 11 is tilled with a mixture of sand and thermosetting resin binder 18 and the` top of the sand mixture in the box is leveled by a scraper 19 to form a at top face 20 substantially parallel with and no lower than the top edge of the side wall 11a. The resin and sand mixture 18 is in dry, pulverulent form and contains the resin-forming ingredients in intimate admixed relationship. A satisfactory sand mixture 18 may have the following composition:

` Percent by weight Silica or Zircon sand 92498 Unset resin or resin-forming ingredients 8-2 the resin material preferably consisting of about 90% by weight phenolic resin in its A or B stage and about 10% by weight of formaldehyde-supplying material such as hexamethylenetetramine.

The sand mixture 18 is prepared by blending the ingredients thereof together until a homogeneous mixture is obtained.

kAfter the scraper 19 forms the level4 top face 2l), a top plate 21is pressed against the top face. 20 of the. sand as shown in Figure 3. This plate 21 has a central aperture 21a for freely receiving the top end of the plug 15. The plate 21 has a pilot portion 2lb fitting snugly` within the removed but preferably should remain in place during curing of the binder.

The pattern box 11, the filler plate 12, the ring patterns 13, the plugs 14, and the plug 15, are preferably of a good heat-conductive metal such as aluminum, steel, or the like, and are heated to temperatures suflicient to set the resin binder. If the plate 21 is to remain in place, it also should be made of similar good heat-conductive material. Resin curing temperatures of from 350-500" F. are satisfactory although any resin-setting temperature may be used depending upon the nature of the resin. The sand and resin mixture is deposited in the heated box 11 and covered with the heated plate 21. After a heating period suticient to convert the resin to the infusible stage, which period is generally only about 1 to 3 minutes, the ejector pins 17 are pushed to discharge a plate mold 22 from the pattern box.

The plate mold 22 asbest shown in Figures 4 and 5 is a generally square plate with a at top 23,. a flat bottom 24, an upstanding peripheral wall 25 extending from around the flat bottom 24 and a four-lobed cloverleafshaped rib 26 defining a ring-shaped molding cavity 27 in each lobe thereof. Each molding cavity has a rectangular cross-section and is joined by gates 28 to a central pour hole or sprue 29 which extends completely through the pattern. A circular rim 30 defines the inner periphery of each, molding cavity 27 and a tapered blind hole 31 is formed at the center of each rib 30. The tapered sides for the holes 31 and' the ribs 26 are provided for ease in removing the pattern from the mold.

As shown in Figures 4 and 5, the portion of each gate cavity 28 adjacent the molding cavity 27, converges in width and in height for ease in removing the casting and to provide that the neck. 28a is narrow to minimize machining at the point where the castings are broken away from the gates.

As shown in Figure 6, a plurality of molds 22 are vertically stacked and are supported by a bottom plate of resin-bonded sand 32 and are held in stacked relation by clamps 33. It will be noted that the sprues 29 of each. mold 22 are aligned to `form a central sprue and a pouring funnel 34 registers with the top sprue 29.

The bottom face 26 of the lowest mold 22 of the stack shown in Figure 6, rests on the at top face of the bottom resin-bonded sand plate 32 while the bottom faces of the successive molds 22 rest on the top faces 23` of the next adjacent mold. The peripheral side walls 25 serve as retainers around the peripheries of the mold cavities 27 and in the event of breakthrough from a mold cavity 27, these walls 25 are eifective to prevent leakage of molten metal out of the assembly. In this manner, breakdown of a mold cavity in any mold plate `vill not interfere'with the formation of good castings in the other cavities of the plates since the space into which the molten metal can flow in the broken mold, will be confined by the side wall. Furthermore, the peripheral side walls contribute to the rigidity desirable for stacking and clamping the individual molds in a composite assembly.

The blind holes 31 in the centers of the ring mold cavities 27 cooperate with the cavity surrounding the mold cavities and bounded by the side Walls 25 to save resin and sand and to provide for uniform curing of the mold. In addition, these holes and this cavity provide for the formation of very permeable mold cavities 27 since each mold cavity 27 is surrounded by only a relatively. thin wall.

It should be understood that any desired number of molds 22 can be stacked with the top face 23 of each mold providing a smooth bottom for the molding cavities in the next adjacent mold. It will also be understood that this invention provides for the formation of resin-bonded sand molds under pressure to produce the desired density and thereby create smoother surfaces than have heretofore been produced in shell molding. It will further be understood that the use of the filler pattern plate andthe plugs for forming holes in the molds, not only result in material saving of mold-forming materials' but also provide for the controlling of the wall thickness of the mold cavities thereby increasing the available permeability of the mold without increasing its bulk or weight. This procedure makes possible the provision of plate molds that can be stacked and have sutiicient strength to withstand rough handling without, however, increasing thicknesses of the parts beyond those thicknesses that are desirable for shell molding. The control of the thicknesses of the various sections of the plate molds insures an even curing of the mold during the setting of the resin.

It will be understood that modications and variations may be elfected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. A shell mold assembly for producing valve seat insert rings which comprises a stack of resin-bonded sand plates each having a at face and an opposed active face with an upstanding peripheral side Wall therearound, said active face having raised ribs in the central portion thereof spaced inwardly from and surrounded by said upstanding side Wall and defining a cloverleaf pattern, circular raised ribs in the central portion of each lobe of said cloverleaf and coacting therewith to deline ring-shaped molding cavities, said plates havingl a hole in each circular rib whereby the molding cavities are defined by concentric ribs of controlled width, each plate having a central sprue therethrough and gate passages radiating therefrom to each molding cavity, means clamping said plates in superimposed stacked relation with the active face of one plate resting upon the at face of the adjacent plate to coact therewith to deine closed molding cavities surrounded by closed blind reservoirs between the molding cavities and the side walls, and said central sprues being aligned to provide a common sprue for the entire stack.

2. The method of making a shell mold of controlled density which comprises depositing a mixture of sand and binder in particulate form in a heated pattern box having an upstanding side wall, mold cavity-defining portions in spaced relation inside of said side wall and a filler plate spaced from said portions and said side wall for limiting the thickness of the portion of the mold surrounding the mold cavity to a thin wall rib, scraping the sand mixture ilush with the top of the pattern box, pressing the sand mixture in the pattern box to compact the sand mixture to the desired density, heating the assembly to set the resin, and stripping the mold from the pattern box.

3. The method of making a shell mold which comprises depositing resin-impregnated sand onto a heated pattern plate, surrounding the mold cavity-forming portions of the plate with an insert plate spaced from said portions to limit the thickness of the cavity-defining Walls, and baking the sand on the plate to produce a shell mold having mold cavity-deiining walls of desired thickness.

4. A shell mold comprising a stack of resin-bonded sand plate molds, each plate mold having a flat face, an upstanding peripheral wall, and ribs within the confines of said wall and spaced therefrom, said ribs defining at least one molding cavity, a gate and a sprue, said peripheral wall and ribs of the plate molds in said stack being in mating contact with the flat faces of the adjacent plate molds, said sprues being in aligned communication in said stack, and means clamping the plate molds in said stack in mated-together relation to define a single sprue hole communicating through gates with a plurality of said molding cavities which are exteriorally surrounded by said ribs and peripheral walls, said peripheral walls being in spaced relation from the ribs surrounding the cavities to provide closed reservoirs receiving molten metal in the event of break-through of the metal from the molding cavities.

5. A sand mold assembly comprising a stack of resinbonded sand mold plates, each plate having an upstanding peripheral wall, a smooth at back face, and ribs defining the mold cavities, said ribs being spaced inwardly from said peripheral side wall, a sprue and a gate for supplying metal to said mold cavities, said sprue and gate being supported inwardly from said side wall, said ribs and side wall terminating in ush relation to provide a flat second face for the plate, means clamping said plates in stacked relation with the side walls and ribs of an upper plate in mated-together contact with the smooth flat back face of the adjacent lower plate whereby the adjacent lower plate coacts with the ribs to complete the mold cavities and coacts with the ribs and side walls to provide sealed reservoirs surrounding the mold cavities and adapted to receive molten metal in the event of break-through of the metal from the mold cavities.

6. A shell mold which comprises a resin-bonded sand plate having a flat back face, an upstanding peripheral wall, and an upstanding rib within the contines of the peripheral wall and spaced inwardly from said peripheral wall to define at least one molding cavity,'said plate being adapted to be stacked with similar plates to provide the back face of one plate as a closure for the molding cavity of the next plate and as a closure for the space between the upstanding peripheral wall and the molding cavity of the next plate to form therewith a closed reservoir surrounding the molding cavity and adapted to receive molten metal from the molding cavity in the event of break-through of the metal from the cavity.

References Cited in the tile of this patent UNITED STATES PATENTS 1,358,435 Frank Nov. 9, 1920 2,081,304 Moluf May 25, 1937 2,654,925 Ensign et al. Oct. 13, 1953 2,726,431 Ensign et al. Dec. 13, 1955 FOREIGN PATENTS 484,930 Great Britain May 12, 1938 683,239 Great Britain Nov. 26, 1952 312,104 Germany May 13, 1919 832,934 Germany Mar. 3, 1952 13,470 Great Britain of 1900 OTHER REFERENCES Am. Foundryman, August 1952, pages 42-46. 

